Just wanted to say that 13 months after the last post here the problem is not resolved in v6.43.14.
Settings windows will stop responding when editing to add information to a device within a submap and once it's back the the Ghost of 4.29 G appears. The window will "hang", but CPU is not adversely affected.
Restarting the server clears the issue, however it'll crop up again on any new devices where I'm adding RouterOS, and sometimes it will appear on Unifi APs (on which I do not enable RouterOS at any point).
It doesn't seem to reoccur on any devices once it's gone, even if I have to manually restart RouterOS on the device.
The only real issue is the delay between double-clicking to open the settings window on a device. The Ghost of 4.29 appears benign and doesn't seem to affect anything at the sub-map level, and doesn't appear to have any effect on whether or not a device shows as "up". If you acknowledge a device with the Ghost of 4.29 on it, that ack on the Ghost of 4.29 G will be persistent and can't be unack'd, but that acknowledgement appears nowhere on the submap view, the map view or on the device icons. It will only appear in the settings window on the device.
All in all, not the worst problem... but the delays can make entering/editing multiple devices a pain. I don't use network discovery and all devices are entered manually as some are "internal" to the client and some are gear on our own network.
I look forward to this being fixed.... someday.