Multi Select Drop Down Field with "Other" value selection

[Sarath]

I have a requirement of making text field hide/unhide when value "Other" is selected on an multi select custom field.

My field "Field A" is a multi-select field with options A,B,C,Other. First I converted this field into multi select dropdown from check-box type by using below line in initializer (Behaviors).

getFieldByName("Field A").convertToMultiSelect()

After that, I used the below code in server-side script by adding a field. There are no errors.

import com.atlassian.jira.component.ComponentAccessor

// Get a pointer to my custom fields
def multisSelectList = getFieldByName("Field A")
def textField = getFieldByName("Other")

// Get the Value of My Select Field
def selectVal = multisSelectList.getValue()

// If the first option is selected in the multi select list then make the text field required.
if(selectVal.toString().contains("Other")){
textField.setHidden(false) // Make text field required
}else{
textField.setHidden(true) // Make text field optional
}

But when I

1. select only "Other" value in Field A, text field appears BUT after selecting Other value and then remove it, the text field still appears.
2. first select values A/B/C and then select "Other", text field appears. Again when I remove "Other" value after selecting it, it won't hide.

And none of the above scenarios are applicable if do not convert the field from checkbox multi select to dropdown multi select. The field behavior is perfect. 

Any help appreciated