Guest Screen Resolution

[BlueLagoon]

Current Configuration
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PC: Dell XPS 15 9530
Host: Windows 10 Home - 64 bit Screen Resolution – 3200 x 1800
Virtual Box version: 5.0.2 r 102096
Guest: Windows 10 Pro – 64 bit Screen Resolution – 1920 x 1440

Issue
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With windows 8.1 (Host and Guest) and VB 5.0.0 r 101573 I could get the same screen resolution in the Guest as per the Host.

When I upgraded the Host, then the Guest to Windows 10 the Guest lost audio and the graphics became quite unstable.

VB 5.0.2 r 102096 came and resolved the audio issue; and the graphics became more stable but I can only get a Guest resolution of 1920 x 1440 and this reduces by 1 on each value, on its own, just about each time I fire-up it up.

Is anyone else having similar problems, and has anyone found a work-around?

Thanking you in anticipation.