ID 391950 - File Browser: Browsing to explicit file path from a previous expression creates extra undo event

Problem summary:

When using the file browser (for example in an AlembicIn node), browsing to an explicit path when the previous path was resolved via expression will create an extra undo event. Expected behaviour would be for a single undo event for setting the field back to constant, and changing the file path.

Steps to reproduce:

1. Add an AlembicIn node and edit it's parameters
2. In the File Section, change the Value Mode to Expression
3. Put a valid expression in the expression textbox (this can just be an explict link to a file)
4. Right Click on the (now highlighted in blue) textbox and choose browse from the context menu
5. Browse to an Alembic file explicitly.

Expected behaviour:

A single undo event should take you from step 4 to step 5.

Actual behaviour:

A check of the Edit/Undo stack will show that 2 Undo events are created:

1. Set Alembic_In.abcAsset
2. Change expression Alembic_In.abcAsset  

Workaround:

No known workaround.

Tested versions/platforms:

• 3.0v9 - Affected