IE7 and Frames Resizing

I have an application that opens in a 3 frame Notes frameset and on an IE6 browser window all 3 frames are resizable (correctly) and do indeed allow resizing both up (making the frame bigger) and down (making the frame smaller). When I open the same application on an IE7 browser, one of the 3 frames will allow resizing down however I can then not make it increase in size. Has anyone else come across this and does anyone have any suggestions as to why?

Frameset properties:

Name: Frameset1

Alias: Home

(all other fields on properties are blank)

Frame1 properties:

Name: FrameA

Type: NamedElement (Page)

Value: Page1

Width: 50%

Scrolling: Default

Allowing Resizing: Yes

3-D border is checked

Border width: Default

(All other settings are either blank or default)

Frame2 properties:

Name: FrameB

Type: Named Element (Form)

Value: Form1

Default target for links in frame: _parent

Width: 50%

Height: 36%

Scrolling: Default

Allow Resizing: Yes

3-D border is checked

Border width: Default

(All other settings are either blank or default)

Frame3 properties:

Name: FrameC

Type: Named Element (Page)

Value: Page2

Default target for links in frame: FrameC

Width: 50%

Height: 65%

Scrolling: Default

Allow Resizing: Yes

3-D border is Checked

Border width: Default

(All other settings are either blank or default)

Thank you for your time and assistance.