1. Open data browser of any table with constraits to othe table
2. Click 'quick edit' on any record
3. Click 'save' (even if you haven't changed something)
4. Selector of constrait is presentend like you are in editing mode
Sorry for my english.
Moving to bugs.
Confirmed in 3.4.x. However, as 3.5.0 was released recently (last 3.4.11-rc1 rollup has been released today), no new bugs will be fixed for 3.4.
The inline editing feature has been superseded by grid editing in 3.5.0, where this bug does not appear. I invite you to upgrade to 3.5 to check out grid editing.