Hiding buttons on custom number pad in iPhone app

Question

I have a custom keypad created from a nib. On a preferences view, users can enter numbers for stream flow warnings. Numbers can be based on cubic feet per second, which is always a positive integer value. Numbers can also be based on stream gauge height, which can be positive or negative floats.

So, I have a custom number pad which has a positive-negative (+/-) button and a decimal point. I need to disable and hide these buttons when the text fields requiring only positive integers are selected.

I have declared properties for these buttons on the view controller that initiates the custom number pad, but calling setHidden or setEnabled has no effect on the state of the buttons at runtime. When supplying these setters values of NO for enabled, and YES for hidden, the buttons are still visible and enabled. The buttons are represented by custom images, but I feel I should be able to hide them in code. Am I missing something?

In the following code sample, I am calling a method that sets some enabled properties of text fields, which all works as planned. Is there something I am missing about setting properties on controls that are part of a seperate nib?

-(void)prefsNotificationChanged{
    NSInteger selection = segNotificationPreference.selectedSegmentIndex;
    switch (selection) {
        case 0:{ // CFS
            [self setInputPrefsFor:txtMinCFS and:txtMaxCFS withLabels:lblMinCFS and:lblMaxCFS forEnabledState:YES];
            [self setInputPrefsFor:txtMinFeet and:txtMaxFeet withLabels:lblMinHeight and:lblMaxHeight forEnabledState:NO];
            [self.btnNumPosNeg setEnabled:NO];
            [self.btnNumPosNeg setHidden:YES];
            break;
        }
        case 1:{ // Gauge Height
            [self setInputPrefsFor:txtMinFeet and:txtMaxFeet withLabels:lblMinHeight and:lblMaxHeight forEnabledState:YES];
            [self setInputPrefsFor:txtMinCFS and:txtMaxCFS withLabels:lblMinCFS and:lblMaxCFS forEnabledState:NO];
            [self.btnNumPosNeg setEnabled:YES];
            [self.btnNumPosNeg setHidden:NO];
            break;
        }
        case -1:{ // None
            [self setInputPrefsFor:txtMinCFS and:txtMaxCFS withLabels:lblMinCFS and:lblMaxCFS forEnabledState:NO];
            [self setInputPrefsFor:txtMinFeet and:txtMaxFeet withLabels:lblMinHeight and:lblMaxHeight forEnabledState:NO];
            break;
        }
        default: break;
    }
}

Property declarations (I have not yet tried implementing states for btnNumDot yet):

@property (nonatomic,strong) IBOutlet UIButton *btnNumDot;
@property (nonatomic,strong) IBOutlet UIButton *btnNumPosNeg;

.m file:

@synthesize btnNumDot, btnNumPosNeg;

Thanks!