Hi,
I tried to reproduce the popup menu problem (at Win7/64, Lazarus 1.8.0, FPC 3.0.4) and I confirm that such behaviour exists.
It is no problem for Lazarus usability or stability. In the future changing focus from designer window/tabsheet back to object inspector (with previously set some filter expression) should, at first, check if filter condition is met (now object inspector enables access to menu items which do not meet filter condition).
For now, use the filter editor in object inspector only when you have tens of components with similar names just to find a proper one and then clear the filter.
WooBean