Bug: Inconsistent Behavior When Using Lakehouse Tables in Warehouse-Scoped Queries in Copy Activity

[Yazdan]

Hi Fabric Team,

I’m writing to report a bug we've encountered while using Microsoft Fabric. we rely on Fabric for our ETL and ELT processes, leveraging both Warehouse and Lakehouse features.

As you know, when setting up a copy activity, we are typically allowed to use a query only on Warehouse, not on Lakehouse tables. However, we discovered that Fabric currently allows users to reference Lakehouse tables in a Warehouse-scoped query, which results in subtle and hard-to-detect issues.

This behavior caused a critical problem in one of our production pipelines: records from yesterday’s load were not copied from Fabric to Oracle. After thorough investigation, we found that the issue stemmed from a query referencing a Lakehouse table, even though the copy activity was configured to use a Warehouse. Fabric did not validate this inconsistency, and as a result, the copy activity silently failed to move the expected data.

This bug could potentially have significant consequences in production environments. I recommend implementing a validation step to ensure that all objects used in a query are consistent with the selected source type (Warehouse vs. Lakehouse), to avoid such hidden issues in the future.

Kind regards,
Yazdan
Data Engineer

[v-prasare]

Hi, We are following up once again regarding your query. Could you please confirm if the issue has been resolved through the support ticket with Microsoft?

If the issue has been resolved, we kindly request you to share the resolution or key insights here to help others in the community. If we don’t hear back, we’ll go ahead and close this thread.

Should you need further assistance in the future, we encourage you to reach out via the Microsoft Fabric Community Forum and create a new thread. We’ll be happy to help.

Thank you for your understanding and participation.

[Yazdan]

Hi,

Thank you for following up.

The issue has not been resolved. I was able to find a temporary workaround for myself by checking the query object directly, but this does not address the root cause of the problem.

I believe this issue still needs to be properly investigated and resolved by Microsoft, as others in the community may also be affected and may not be able to apply the same workaround.

Appreciate your continued support.

Best regards,
Yazdan Aghajanian

[burakkaragoz]

Hi @Yazdan ,

Thanks for flagging this—this definitely sounds like a sneaky and potentially dangerous issue 😬

You're absolutely right: if a Copy Activity is scoped to Warehouse, it shouldn’t silently allow Lakehouse tables in the query. Even if it technically works in some cases, the lack of validation can lead to hard-to-detect bugs like the one you experienced.

A few thoughts:

• Until this is addressed, it might be safer to strictly separate Lakehouse and Warehouse logic in your pipelines.
• You could also consider adding a manual validation step in your process to catch any cross-environment references before deployment.
• Totally agree that Fabric should implement a validation layer here—it would save a lot of headaches in production.

Appreciate you sharing this—it’ll definitely help others avoid the same trap.

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If my response resolved your query, kindly mark it as the Accepted Solution to assist others. Additionally, I would be grateful for a 'Kudos' if you found my response helpful.

[Yazdan]

Hi,

Yes, I had previously implemented a workaround to identify the issue, and I’ve also raised a support ticket with Microsoft — Service Request #: 2505130030000051. I'm currently waiting for their response.

I completely agree with your points—having proper validation between Warehouse and Lakehouse environments would definitely help avoid these subtle and potentially risky issues. Hopefully, this gets addressed soon.

Thanks again for your insights and support!

Best regards,
Yazdan Aghajanian

[v-prasare · Accepted solution]

Hi @Yazdan , 

In this scenario i suggest you to raise a support ticket here. so, that they can assit you in addressing the issue you are facing. please follow below link on how to raise a support ticket:

How to create a Fabric and Power BI Support ticket - Power BI | Microsoft Learn

Thanks,

Prashanth Are

[Yazdan]

Hi,

Thank you for your suggestion.

I have already raised a support ticket with Microsoft — Service Request #: 2505130030000051 — and I’m currently waiting for their response.

I’ll share any updates or resolutions here once I hear back.

Best regards,
Yazdan Aghajanian

[Yazdan]

Hi,

Thank you for your suggestion.

I have already raised a support ticket with Microsoft — Service Request #: 2505130030000051 — and I’m currently waiting for their response.

I’ll share any updates or resolutions here once I hear back.

Best regards,
Yazdan Aghajanian